This invention relates to an apparatus for braking of a train of vehicles consisting of a tractor vehicle and at least one trailer vehicle.
Braking a train of road vehicles, e.g., a tractor and semitrailer or a truck with one or more trailers, presents great technical problems, especially when the road is slippery. Due to unequal braking forces at the individual wheels or to different friction conditions between the wheels and the road, there is a risk of the vehicles skidding and the rear vehicle fishtailing or, more seriously, the whole train jackknifing. Once the vehicle train has started to skid, it is almost impossible for a driver to regain control.
Up to now, efforts have been concentrated on preventing the onset of skidding by means of ingenious brake designs. In some systems the braking pressure delivered to each wheel brake has been individually controlled, in the same manner as with the well known anti-skid systems for airplanes. (See, for example, the aircraft anti-skid systems in U.S. Pat. No. 2,957,658; No. 2,957,659; No. 2,869,807; and No. 3,017,145). Such systems continuously sense the rate of rotation and/or the rate of change of rotation of the individual wheels. The measured rates or changes in rates of rotation are compared with each other and/or with the actual speed or deceleration of the vehicle. The pressure applied to each individual wheel brake then is released or otherwise adjusted if the speed of the wheel falls below the speed of the other wheels or inertial sensors detect an incipient skid; so that the rate of rotation of the wheel is just the permitted limit value at which optimal braking is obtained without the wheels being locked or a skid developing. However, these systems have shown an unfortunate tendency to oscillate, due to, among other things, interaction with the natural frequency of the wheel suspension and the large number of wheels in a train of vehicles as compared with an airplane. Furthermore, providing a brake control system for each wheel of a tractor-trailer combination is very expensive.